A turbocharger is known as a supercharger used as a means for improving the power output and performance of an automobile engine. This turbocharger is an apparatus for bringing the engine into a supercharged state in which more air is supplied to the engine than its natural intake by rotating a compressor, using power output from a turbine that is driven by exhaust energy of the engine. When the engine is running at a low rotational speed, the exhaust turbine hardly works due to the reduced flow rate of exhaust gas, and therefore, with an engine capable of rotating in a high rotational speed range, this turbocharger inevitably involves a slow-moving feeling until the turbine starts rotating efficiently, as well as a so-called turbo-lag or time required afterwards until the turbine rapidly reaches its full-running state. Moreover, with a diesel engine that runs inherently at a low rotational speed, there is a drawback that the turbocharger effect can hardly be achieved.
Because of this, a VGS type turbocharger (VGS unit) that works efficiently even when the engine is running in a low rotational speed range has been developed. This turbocharger suitably throttles a low flow rate of exhaust with adjustable blades (vanes) to increase the velocity of the exhaust and to increase the work amount of the exhaust turbine, thereby enabling the engine to output high power even when the engine is running at a low rotational speed. Therefore the VGS unit requires an additional adjustment mechanism or the like for the adjustable blades, and also peripheral constituent components have to have a more complex shape or the like than conventional ones.
Under the circumstances, the assignee of the present application has undertaken rigorous research and development on VGS type turbochargers and has filed many patent applications (see, for example, Patent documents 1 to 8).
Meanwhile, an exhaust guide assembly of such a VGS type turbocharger is provided with an adjustment mechanism (drive ring) for concurrently and evenly opening and closing a plurality of circumferentially equally arranged adjustable blades. Namely, upon receipt of power of a shifting drive from an actuator provided outside, the adjustment mechanism including the drive ring first starts rotating, which eventually causes the plurality of adjustable blades to concurrently and evenly open and close (rotate).
Since the turbocharger is repeatedly used under extremely severe environments with high temperatures and exhaust gas, and since the adjustable blades control the flow rate of exhaust gas by their degree of opening, the adjustable blades during the operation are greatly subjected to the force of exhaust gas. Therefore, when rotating the adjustable blades, an excessive force is applied to the drive ring 31′ that receives the power of the shifting drive from the actuator AC, in particular an input portion 36′ where the power of the shifting drive is input, and, in combination with the above-mentioned environmental conditions, this portion is exposed to even more severe environments. Accordingly, the input portion 36′ of the drive ring 31′ sometimes suffers wear (wastage) after years of use in which the material of this portion is partly gouged out, or sheared off as is shown as one example in FIG. 14(a). Therefore a technique for improving (reinforcing) wear resistance of the input portion 36′ has been desired.
To suppress such wear as much as possible, a technique of enhancing the entire wear resistance of the drive ring 31′ by increasing its entire sheet thickness, or a technique of increasing the wear resistance by reviewing the material quality and changing the material itself used for the drive ring 31′, or the like, may be considered.
However, the above-mentioned wear is not a phenomenon that occurs in the entire drive ring, but a phenomenon that occurs particularly in the input portion 36′ that receives the power of the shifting drive from the actuator AC. Thus, the technique of increasing the entire sheet thickness of the drive ring 31′ would be an attempt to reinforce the parts in addition to the input portion 36′, which is unnecessary, as it were, and would lead to an increase in weight or cost and could not be adopted easily. At any rate, in the industry of automobile parts of this kind, cost reduction, weight reduction, and space reduction are constant requirements and therefore this technique of increasing the entire sheet thickness is contrary to these requirements, and thus not realistic.
On the other hand, the technique of changing the material itself used for the drive ring 31′ to a material having a high wear resistance also involves a cost increase, and therefore is not an easily adoptable technique, under the circumstances of the automobile parts industry where cost reduction is a constant requirement.
The input portion 36′ of the drive ring 31′ often includes a slit-like drive opening 36a′ for receiving a shift transmitting member on the actuator side. There has been an attempt in which, instead of punching out an opening, for example as shown in FIG. 14(b), part of the blank material B′ is made to stand (bend) at about 90° relative to the actual product part, and is used for the reinforcement of the input portion 36′. However, since the drive opening 36a′ of the input portion 36′ has a limited (small) width S in the first place, standing up this part with such a dimension could not sufficiently increase the wear resistance of the input portion 36′.
In view of this, under the circumstances, a technique is adopted in which a separate member p for the reinforcement is attached to the input portion 36′ of the drive ring 31′ by welding or the like, for example as shown in FIG. 14(c), to partially improve the wear resistance of the input portion 36′. However, this technique requires an additional separate member p, and further, this separate member p needs to be joined by welding or the like (attached afterwards), and so the number of process steps in the production stage is inevitably increased. Thus, in the automobile industry where price competition is intense, a further improved technique that can replace this technique has been desired.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 2003-49655    Patent document 2: Japanese Patent Application Laid-Open Publication No. 2003-49663    Patent document 3: Japanese Patent Application Laid-Open Publication No. 2003-49656    Patent document 4: Japanese Patent Application Laid-Open Publication No. 2003-49657    Patent document 5: Japanese Patent Application Laid-Open Publication No. 2003-49658    Patent document 6: Japanese Patent Application Laid-Open Publication No. 2003-49659    Patent document 7: Japanese Patent Application Laid-Open Publication No. 2003-48033    Patent document 8: Japanese Patent Application Laid-Open Publication No. 2003-49660